Use IOFile for TextureToPng to support non-ascii

Changed save texture/screenshot uses to std::string
Removed unneeded new/delete calls when dealing with temp data.

Source/Core/VideoCommon/Src/ImageWrite.h

@@ -8,7 +8,7 @@
 #include "Common.h"
 
 bool SaveData(const char* filename, const char* pdata);
-bool TextureToPng(u8* data, int row_stride, const char* filename, int width, int height, bool saveAlpha = true);
+bool TextureToPng(u8* data, int row_stride, const std::string filename, int width, int height, bool saveAlpha = true);
 
 #endif  // _IMAGEWRITE_H